The present invention relates to compositions for optical fiber coatings and fiber optic ribbon matrices, optical fibers that contain a secondary coating prepared from such compositions, methods of making such optical fibers, and fiber optic ribbons that contain a matrix prepared from such compositions.
Optical fibers have acquired an increasingly important role in the field of communications, frequently replacing existing copper wires. This trend has had a significant impact in local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications has begun and is expected to increase.
Optical fibers typically contain a glass core and cladding, and at least two coatings, e.g., a primary (or inner) coating and a secondary (or outer) coating. The primary coating is applied directly to the glass fiber and, when cured, forms a soft, elastic, and compliant material which encapsulates the glass fiber. The primary coating serves as a buffer to cushion and protect the glass fiber core when the fiber is bent, cabled, or spooled. The secondary coating is applied over the primary coating and functions as a tough, protective outer layer that prevents damage to the glass fiber during processing and use.
Certain characteristics are desirable for the secondary coating. Before curing, the secondary coating composition should have a suitable viscosity and be capable of curing quickly to enable processing of the optical fiber. After curing, the secondary coating should have the following characteristics: sufficient stiffness (i.e., modulus) to protect the encapsulated glass fiber yet enough flexibility (i.e., elongation) for handling, low water absorption, low tackiness to enable handling of the optical fiber, chemical resistance, and sufficient adhesion to the primary coating.
To achieve the desired characteristics, conventional secondary coating compositions generally contain-urethane-based oligomers in large concentration, with monomers being introduced into the secondary coating composition as reactive diluents to lower the viscosity. Because conventional oligomeric components are, in general, much more expensive than the monomeric components, the use of oligomers in high concentration has the effect of increasing the cost of producing secondary coating compositions as well as the resulting optical fiber. Despite the cost of using oligomeric components in high concentration, it is believed that there are no commercially viable secondary coating compositions that either contain a low concentration or are completely devoid of oligomeric components.
Thus, there remains a need for suitable secondary coating compositions which can be prepared at lower cost than conventional secondary coating compositions and yield secondary coatings with a suitable modulus and other physical properties.
There is also a need for a coating that will reduce the sensitivity of the fiber to bending, particularly microbending. This is especially relevant for high data rate optical fiber. A high data rate fiber is typically a single mode fiber with a large effective area. Fibers with a large effective area have an increased signal mode transmission capacity in comparison to non-large effective area fibers. However, fibers with a large effective area have a greater sensitivity to stresses, such as stresses caused by bending the fiber. These stresses can lead to distortion of the optically active region of the fiber and result in microbend signal attenuation. There is a further need for a secondary optical fiber coating that has low shrinkage properties.
The present invention relates to a composition for coating optical fibers and optical fibers coated with the composition. A first embodiment of the inventive coating composition comprises at least one component having at least one acrylate functional end group and at least one heterocyclic moiety capable of undergoing ring opening polymerization, preferably the one component comprises either a monomer or an oligomer and wherein a Young""s Modulus of said composition when cured comprises at least about 100 MPa. A further embodiment of the invention includes an optical fiber coated with the first embodiment of the inventive coating composition.
A second embodiment of the inventive coating composition comprises at least one component having at least one acrylate functional end group and a second component comprising at least one heterocyclic moiety capable of undergoing ring opening polymerization, wherein a Young""s Modulus of said composition when cured comprises at least about 100 MPa. An additional embodiment of the invention comprises an optical fiber coated with the second embodiment of the inventive coating composition.
The composition of the present invention has suitable characteristics which enable its use in preparing the outer coating material on optical fibers and the matrix material on fiber optic ribbons. Moreover, when cured, the composition results in a coating or matrix material that possesses desirable characteristics with respect to water absorption, reduced microbend sensitivity, and lower extractables, as well as strength or modulus.
An advantage of the inventive coating composition is that the composition has low shrinkage stress due to its low cure shrinkage characteristics. The shrinkage stress applied to fiber due to the curing of the coatings is a product of the Young""s modulus and the degree of shrinkage of the secondary coating, and the cross sectional area of the coating layer. The inventive coating will minimize the stress applied to the fiber by reducing the shrinkage the coating will exhibit during curing. A fiber coated with the inventive composition has improved microbend attenuation performance. Also a fiber coated with the inventive coating will not exhibit delamination between a primary coating and the inventive coating. Another advantage of the inventive composition is that composition may utilize ring opening polymerization and may also utilize free radical polymerization in combination with ring opening polymerization. Preferably the ring opening polymerization occurs simultaneously or after the free radical polymerization has initiated. Additionally the cured inventive coating can have a high modulus and a satisfactory cure speed.